This invention relates to an exhaust braking control apparatus for controlling exhaust gas flow through an engine exhaust passage to provide an engine braking effect.
It is the current practice to increase an engine braking effect by using a control valve to close the engine exhaust passage, causing the engine to operate like a compressor. For example, Japanese Patent Kokai No. 2-78741 discloses a conventional exhaust braking control apparatus including an exhaust braking inhibit circuit arranged to inhibit the exhaust braking operation during a change produced in the automatic transmission from a higher gear to a low gear for engine braking. This is effective to decrease the engine reversed driving force and thus the shock produced during a gear shifting operation. The working fluid pressure used in the automatic transmission for the gear shifting operation is set at an appropriate level suitable in the absence of the exhaust braking operation. Thus, the torque capacity required during the gear shifting operation for the clutches and brakes provided in the automatic transmission will be short to cause serious problems if the exhaust braking operation continues during the gear shift operation because of a failure of the exhaust braking inhibit circuit.